Projection lens device and projection display apparatus using the same

Abstract

A projection lens device includes, in order from a magnification side, a first lens group G₁ having a negative refractive power, and a second lens group G₂ having a positive refractive power. The projection lens device is substantially telecentric on a reduction side thereof. The second lens group G₂ includes a three-element cemented lens L₁₀ to L₁₂ formed by cementing three lens elements. A space between the first lens group G₁ and the second lens group G₂ is set as the maximum inter-lens space (the maximum air space) so that a reflection mirror 4 can be inserted. Also, the projection lens device satisfies eight conditional expressions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is based upon and claims the benefit of priority from the Japanese Patent Application No. 2007-134538 filed on May 21, 2007; the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Technical Field[0003]The invention relates to a projection lens device for magnifying and projecting display information and the like from a light valve such as a transmissive or reflective liquid crystal display device or a DMD (a digital micro mirror device), and in particular, relates to a projection lens device suitable for a rear projection display apparatus such as rear projection televisions, and a projection display apparatus using the projection lens device.[0004]2. Description of the Related Art[0005]Known projection display apparatuses include (i) a front projection display apparatus in which a projection lens device is arranged on the same side as a viewer, the front projection display a...

AI Technical Summary

Benefits of technology

[0033]Since the projection lens device according to the invention has the above configuration, the projection lens device can secure a long back focal length and have a wide angle of view and high projection performance. Also, when a reflective element for deflecting an optical path is used in order to achieve miniaturization, it is possible to use an inexpensive reflection mirror as the reflective element, which can decrease manufacturing cost.

[0034]Furthermore, the projection display apparatus according to the invention can be configured to secure a long back focal length, have a wide angle of view and high projection performance, and decrease manufacturing cost.

Problems solved by technology

However, U.S. Pat. No. 7,123,426, and U.S. Pat. No. 7,126,767 fail to have a concept of inserting a reflective element into an optical path.

Also, in order to compensate for a narrow space, JP 2003-15033 A and JP 2004-326079 A uses a prism for lengthening an optical path, in stead of a reflection mirror, as a reflective element inserted into the optical path, which increases a manufacturing cost.

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